Previous reports have linked hypoxia-induced marrow proliferation with a simultaneous increase in the uptake of Gallium-67m in the bone marrow. The purpose of this study is to determine the effects of hypoxia on Ga-67m distribution in other tissues of normal and tumor-bearing mice. Radioactivity in various tissues was determined 24 hours after injecting the test mice with 5 microcuries of Ga-67m citrate. Normal male mice treated with either a continuous hypoxic atmosphere or phenylhydrazine showed a reduction in radioactivity in plasma and tissues after one to two days. After this initial decrease, the levels of Ga-67m in plasma and tissues increased with a concomitant rise in hematocrit. After five to seven days, the labeling of tissues of hypoxia treated animals was greater than that of control animals. However, mice bearing tumors arising from injection of Kirsten virus transformed mouse cells showed less change in the tissue uptake of Ga-67m when placed in a hypoxia atmosphere. In contrast to that of normal animals, the plasma Ga-67m level was initially low in tumor-bearing mice, but rose with increasing hematocrit. BIBLIOGRAPHIC REFERENCES: Tyndall, R.L., S.J. Chaskens, J.E. Carlton, Bill Nelson and J.C. Daniel. 1976. Gallium-67 Distribution in Pregnant Mammals. J. Exp. Zool. v. 195. No. 3, March. Yang, Wen-Kuang, R.L. Tyndall, and J.C. Daniel, Jr. 1976. DNA-and RNA-Dependent DNA Polymerases: Progressive Changes in Rabbit Endometrium During Preimplantation State of Pregnancy. Biology of Reproduction 15, 604-613.